Re: [PATCH v3 1/3] kprobes: Add text_alloc() and text_free()

From: Kees Cook <keescook@chromium.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	linux-kernel@vger.kernel.org, x86@vger.kernel.org,
	Andi Kleen <ak@linux.intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jessica Yu <jeyu@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
	Will Deacon <will@kernel.org>,
	Sami Tolvanen <samitolvanen@google.com>,
	Alexandre Ghiti <alex@ghiti.fr>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Peter Collingbourne <pcc@google.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	Arnd Bergmann <arnd@arndb.de>, Stephen Boyd <sboyd@kernel.org>,
	Andy Lutomirski <luto@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Miroslav Benes <mbenes@suse.cz>, Babu Moger <Babu.Moger@amd.com>,
	Omar Sandoval <osandov@fb.com>, Nayna Jain <nayna@linux.ibm.com>,
	Marco Elver <elver@google.com>, Brian Gerst <brgerst@gmail.com>,
	Jiri Kosina <jkosina@suse.cz>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	Mike Rapoport <rppt@linux.ibm.com>
Subject: Re: [PATCH v3 1/3] kprobes: Add text_alloc() and text_free()
Date: Wed, 15 Jul 2020 12:38:19 -0700	[thread overview]
Message-ID: <202007151236.FE6CA96261@keescook> (raw)
In-Reply-To: <20200715172732.35110a4e53e84fcec9aeac83@kernel.org>

On Wed, Jul 15, 2020 at 05:27:32PM +0900, Masami Hiramatsu wrote:
> 
> On Wed, 15 Jul 2020 01:32:27 +0300
> Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> wrote:
> > [...]
> > -void *module_alloc(unsigned long size)
> > -{
> > -	void *p;
> > -
> > -	if (PAGE_ALIGN(size) > MODULES_LEN)
> > -		return NULL;
> > -
> > -	p = __vmalloc_node_range(size, MODULE_ALIGN,
> > -				    MODULES_VADDR + get_module_load_offset(),
> > -				    MODULES_END, GFP_KERNEL,
> > -				    PAGE_KERNEL, 0, NUMA_NO_NODE,
> > -				    __builtin_return_address(0));
> > -	if (p && (kasan_module_alloc(p, size) < 0)) {
> > -		vfree(p);
> > -		return NULL;
> > -	}
> > -
> > -	return p;
> > -}
> 
> Please don't touch this module_alloc() at all. Then we can
> just call __vmalloc_node_range() in the text_alloc().

Hm? I thought the requirement was that trampolines needed to stay within
a certain distance of kernel text and that the module_alloc() enforced
that?

-- 
Kees Cook